When displaying character or other on-screen display symbols on the screen of a television receiver or monitor, it is necessary that the OSD micro processor be properly synchronized with the horizontal and vertical synchronizing components of the video signal being displayed. Generally speaking, this synchronization is achieved by deriving horizontal synchronizing pulses from the line deflection circuitry of the receiver or from the heater voltage for the picture tube. Typically, vertical synchronization pulses for OSD use are derived from the vertical flyback pulse of the receiver vertical deflection system.
Generally speaking, the foregoing method of OSD synchronization gives adequate performance under most operating conditions. However, under some circumstances (e.g., poor signal to noise, or deflection instabilities), the conventional technique of OSD synchronization may produce erratic results due to instabilities in the deflection horizontal and vertical synchronizing signals and, as a result, displayed characters may exhibit jitter or other instabilities.